Refractory structure for a rotary kiln



Oct. 10, 1967 J. MARTiNET ET AL 3,346,248

REFRACTORY STRUCTURE FOR A ROTARY KILN 2 Sheets-Sheet 1 Filed May 19, 1965 INVENTORX JACQ R. MARTINET BY JA 0- HICKS I Attorney Oct. 10, 1967 R MARTlNET ET AL 3,346,248

REFRACTORY STRUCTURE FOR A ROTARY KILN Filed May 19, 1965 V 2 Sheets-Sheet 2 INVENTORS JACQUES R. MARTINET JAMES C. HICKS United States Patent 3,346,248 REFRACTORY STRUCTURE FOR A ROTARY KILN Jacques R. Martinet, San Jose, and James C. Hicks, Los

Altos, Calif assignors to Kaiser Aluminum & Chemical Corporation, Oakland, Calif., a corporation of Delaware Filed May 19, 1965, Ser. No. 457,111 14 Claims. (Cl. 263--33) ABSTRACT OF THE DISCLOSURE A structure for the refractory lining of rotary kilns, for example cement kilns, is disclosed. The lining is made of refractory shapes having complementarily shaped protuberances and recesses on their opposite side faces. In addition, the refractory shapes have thermal expansion allowance means on the side faces adjacent the hot ends and, adjacent the cold ends, spacer plates made of a material, for example steel, which will withstand a temperature of about 1000 F. without decomposing.

This invention concerns rotary kilns and refractory linings therefor.

It has long been recognized that in lining a rotary kiln with refractory material, account must be taken of the thermal expansion of the refractory upon heating the kiln to its operating temperature. It has been the practice in the past, particularly when the lining was made of basic or non-acid materials such as periclase or mixtures of periclase and chromite, to insert metal plates, for example steel, between the refractory blocks making up the lining. Upon heating of the lining, the steel oxidizes and/ or melts, the oxide being absorbed into the refractory, thus providing room for expansion of the refractory into the space formerly occupied by the metal. However, there have been several problems with such prior art structures.

First, there is an intermediate range of temperatures, between about 1500 F. and about 2200 F., where the steel plates oxidize and expand to two or three times their former thickness but are not yet absorbed by the refractory. Thus, there often occurs at an intermediate point in the furnace lining, between the hot face, where the steel plates have completely disappeared through oxidation, absorption, and/ or melting, and the cold face, where substantially no oxidation or expansion has taken place, a region of high stress in the lining believed substantially due to expansion of the metal plate. It is not uncommon for the lining to rupture in this intermediate zone with consequent falling away and loss of large sections of brick.

A second problem results from the present trend in the industry to build larger diameter kilns than heretofore generally used. Since in these larger kilns it is not the practice to proportionately increase the thickness of the refractory lining, the stresses due to thermal expansion and oxidation expansion become of greater significance. In other words, the same absolute thickness of refractory lining in a larger diameter kiln leads to a relatively thinner lining which must bear increased expansion stresses, due to the greater lineal length of refractory about the circumference of the kiln.

Third, there has also occurred in recent years a trend toward the use of the newer high fired or directbonded type of refractories consisting essentially of mixtures of periclase and chrome ore. These refractories have been fired to such a temperature that a direct bond has developed between the periclase and chromite grains in the refractory, the relatively less refractory silicate gangue material occurring interstitially in discrete discontinuous pockets. Direct bonding provides greatly increased hot strength in these refractories. However, high fired refractories show less tendency to absorb iron oxide and less tendency to deform plastically under stresses at high temperatures. Accordingly, they continue to expand up to higher temperatures under load and the problems of thermal and oxidation expansion are more critical in a lining made from highfired refractories.

Prior attempts have been made to solve the foregoing problems. For example, it is known to place a combustible sheet, such as paper or cardboard, between the metal plate and the refractory block making up the kiln lining. Combustion of this paper or cardboard, together with that of any glue used to hold the plate and combustible on the refractory block, provides room for expansion. It has been found that up to about one-third the total amount of thermal expansion required by the refractory can be provided by this combustible material the remainder being provided by the thickness of the metal itself. If a greater amount of combustible than this is used it has been found that the lining becomes too loose during heating up of the rotary kiln since the combustible disappears before the refractory is hot enough to expand into the space provided. The loose lining can, under some conditions, actually fall out of place. The problem is particularly acute with larger kilns or if there are any delays in the heating up of the refractory lining.

There is now provided, according to this invention, a refractory lining for a rotary kiln which overcomes the foregoing problems. According to this invention, a rotary kiln is lined with refractory blocks having, on their abutting side faces and adjacent their inner or hot ends or faces, thermal expansion allowance means such as paper, cardboard, or asbestos, and adjacent their outer or cold ends or faces spacer means such as steel plates or asbestos strips, and intermediate these, mechanical interlocking or retention means, for example a tongue and groove complementary structure on adjacent blocks.

An illustrative but non-limiting example of a structure according to this invention is shown in the drawing, in which:

FIGURE 1 shows a refractory block for use in a construction according to this invention;

FIGURE 2 shows a transverse cross-section of a portion of a rotary kiln constructed according to this invention;

FIGURE 3 shows an end view of an alternative embodiment; and

FIGURE 4 shows a side view of the alternative structure.

The refractory block 11 of this invention is wedgeshaped and is similar to conventional refractory block used for lining rotary kilns in that it has an inner end or face 12, an outer end or face 13, and two pairs of opposed side faces, the first pair, 15 and 1-6, being substantially parallel and the second pair, 17 and 18, converging toward inner end 12. In side face 17 of the second pair there is a recess, a rounded groove or recess 20 extending from side face 15 to side face 16 being shown. Preferably, this recess is placed closer to outer end 13 than to inner end 12. On side face 18 of the second pair there is a protuberance of form and location complementary to that of the recess so that when refractory units 11 are placed adjacent each other the protuberance of one will lie and fit within the recess of an adjacent unit. In the figure, the protuberance is shown in the form of a rounded boss or rib 21 extending along side face 18 from side face 15 to side face 16.

On one of the second pair of side faces, and adjacent inner end 12 of the refractory block, is placed a thermal expansion allowance means, strip 23 being shown on face 17 in the drawing. This thermal expansion allowance means can be a combustible such as paper or cardboard or a material such as asbestos which will decompose and/ or melt or soften upon heating and compress under pressure. The thickness of the thermal expansion means will be such as to provide the requisite space for thermal expansion of the refractory at inner end 12 upon heating of the refractory to the operating temperature of the furnace, as is well understood in the art. Excessive thermal expansion allowance is to be avoided since it is desirable that, at operating temperature, the refractory blocks be under slight compressive stress to hold them in position as the kiln rotates.

On one of the second pair of side faces, adjacent the outer end of the refractory block, there is placed a spacer strip, strip 24 being shown on face 17 adjacent outer end 13. This spacer strip is made of a material which will withstand a temperature of at least about 1000 F. without decomposition. It can be, for example, a metal plate, such as a steel plate, or an asbestos strip. If desired, spacer 24, if made of metal, can be corrugated or embossed or made of wire mesh so as to provide for thermal expansion by crushing when the outer end of the refractory block is heated up as the lining wears away during use of the kiln.

FIGURE 2 shows a section of a rotary kiln incorporating a lining constructed according to this invention and using refractory units such as described above. Refractory units 11 are laid with their outer ends or faces 13 abutting the metal kiln shell 25, as is customary in the art. Inner ends or faces 12 are disposed toward the interior of the rotary kiln where they are exposed to high temperatures when the kiln is in operation. Thermal expansion allowance means 23 and spacers 24 lie between adjacent refractory units 11 and the recess 20 of one refractory unit has disposed within it the protuberance 21 of the adjacent unit. It will be understood that strips 23 and 24 need not be attached to refractory units 11, but can be placed between such units during the construction of the kiln lining. However, it will generally be found more convenient to attach the strips directly to the refractory units before they are placed in the kiln.

When paper is used forexpansion strips 23, there may also be placed, as is shown in FIGURE 2, strips 27 of material such as asbestos between refractory shapes 11 and lying between strips 23 and recesses 20 and protuberances 21. The purpose of strips 27 is to prevent granular material from the rotary kiln falling into the spaces between refractory units 11 after thermal expansion strips 23 have disappeared. Were such granular material to fall into the cracks between the refractory units, it could prevent expansion of these units upon further heating and cause stresses which would rupture the lining.

It will be noted that the recesses or grooves 20 and protuberances or ribs 21 are so disposed that there is no line contact between them which could cause areas of concentrated stress which might rupture the lining. This can be achieved by making the recess and protuberance of precisely the same size and shape or by making the recess somewhat larger than the protuberance. The purpose of the interlocking protuberances and recesses is to prevent radial displacement of refractory blocks 11, with consequent collapse of the lining, during the early and intermediate stages of the heating-up process, before the lining is fully expanded.

Alternatively, as shown in FIGURES 3 and 4, the protuberance can take the form of one or more hemispherical bosses 28 and the recess can be in the form of one or more complementarily shaped and located hemispherical recesses 29. Although one boss and one recess can be placed on the side of a shape, if two are placed on each side, as shown in FIGGURE 4, then such shapes can be placed in staggered or joint-overlapping relationship in lining the kiln, if desired.

The structure of the present invention is useful for lining rotary kilns such as cement kilns, lime kilns, and any other kiln of circular construction which is rotated about its axis during its operation. It is an advantage of construction according to this invention that by it there is provided a kiln lining which provides correct thermal expansion allowance and thus overcomes the problem of pinching and spalling of the refractory lining and which, at the same time, provides a stable structure which will not collapse during the heating-up of the furnace.

It will be understood that the above specific description and figures have been given for purposes of illustration only and that variations and modifications can be made therein without departing from the spirit and scope of the appended claims.

Having now described the invention,

What is claimed is:

1. A rotary kiln comprising a cylindrical metal shell and a refractory lining within said shell, said lining including: refractory blocks having an inner end, an outer end, and two opposed pairs of side faces, the first opposed pair being substantially parallel and the second opposed pair converging toward said inner end, one side face of said second pair having a recess and the other side face of said second pair having a protuberance, said protuberance being of complementary form and location to said recess, whereby the protuberance of one block is disposed within the recess of an adjacent block; thermal expansion allowance means located between the converging side faces of adjacent blocks adjacent the inner ends thereof and terminating short of said recesses and protuberances; and spacers, adapted to withstand a temperature of about 1000 F. without decomposition, disposed between said converging faces of adjacent refractory blocks adjacent their outer ends and terminating short of said recesses and protuberances.

2. A rotary kiln according to claim 1 wherein said protuberances and said recesses are located closer to the outer ends than the inner ends of said blocks.

3. A rotary kiln according to claim 2 containing in addition asbestos strips disposed between the second side faces of adjacent refractory blocks between the thermal expansion means and the protuberances and recesses.

4. A rotary kiln according to claim 1 wherein said recesses are in the form of rounded grooves.

5. A rotary kiln according to claim 4 wherein said rounded grooves extend the full distance between said first pair of side faces.

6. A rotary kiln according to claim 1 wherein said recesses and protuberances are free of stress-creating line contact.

7. A rotary kiln according to claim 1 wherein said thermal expansion allowance means is paper.

8. A rotary kiln according to claim 1 wherein said thermal expansion allowance means is asbestos.

9. A rotary kiln according to claim 1 wherein said spacers are made of steel.

10. A rotary kiln according to claim 9 wherein said steel spacers are embossed to provide high temperature thermal expansion allowance.

11. A rotary kiln according to claim 1 wherein said spacers are made of asbestos.

12. A wedge-shaped refractory block having a smaller inner end face, a larger outer end face, and two opposed pairs of side faces, the first opposed pair being substantially parallel and the second opposed pair converging toward said inner end face, one side face of said second pair having a recess and the other side face of said second pair having a protuberance, said protuberance being adapted to fit in complementary relationship with the recess in a like refractory block when disposed in a cylindrical furnace lining; thermal expansion allowance means located on at least one of said second pair of side faces adjacent the inner end of the block and terminating short of said recess and protuberance; and a spacer, adapted to withstand a temperature of 1000 F. without decomposition, located on at least one of said second pair of side faces adjacent the outer end of said block and terminating short of said recess and protuberance.

13. A refractory unit according to claim 12 wherein said recess is in the form of a rounded groove extending between the first two side faces.

14. A wedge-shaped refractory block having a smaller inner end face, a larger outer end face, and two opposed pairs of side faces, the first opposed pair being substantially parallel and the second opposed pair converging toward said inner end face, one side face of said second pair having a rounded groove extending between the first two side faces and the other side face of said second pair having a rounded rib adapted to fit in complementary relationship with the rounded groove in a like refractory block when disposed in a cylindrical furnace lining, said groove and said rib being located closer to said outer end than said inner end; cardboard thermal expansion allowance means located on at least one of said second pair of side faces adjacent the inner end of the block and terminating short of said recess and protuberance; and a steel spacer located on at least one of said second pair of side faces adjacent the outer end of said block and terminating short of said recess and protuberance.

References Cited FREDERICK L. MATTESON, JR., Primary Examiner.

JOHN J. CAMBY, Examiner. 

1. A ROTARY KLIN COMPRISING A CYLINDRICAL METAL SHELL AND A REFRACTORY LINING WITHIN SAID SHELL, SAID LINING INCLUDING: REFRACTORY BLOCKS HAVING AN INNER END, AN OUTER END, AND TWO OPPOSED PAIRS OF SIDE FACES, THE FIRST OPPOSED PAIR BEING SUBSTANTIALLY PARALLEL AND THE SECOND OPPOSED PAIR CONVERGING TOWARD SAID INNER END, ONE SIDE FACE OF SAID SECOND PAIR HAVING A RECESS AND THE OTHER SIDE FACE OF SAID SECOND PAIR HAVING A PROTUBERANCED, SAID PROTUBERANCE BEING OF COMPLEMENTARY FORM AND LOCATION TO SAID RECESS, WHEREBY THE PROTUBERANCE OF ONE BLOCK IS DISPOSED WITHIN THE RECESS OF AN ADJACCENT BLOCK; THERMAL EXPANSION ALLOWANCE MEANS LOCATED BETWEEN THE CONVERGING SIDE FACES OF ADJACENT BLOCKS ADJACENT THE INNER ENDS THEREOF AND TERMINATING SHORT OF SAID RECESSES AND PROTUBERANCES; AND SPACERS, ADAPTED TO WITHSTAND A TEMPERATURE OF ABOUT 1000*F. WITHOUT DECOMPOSIITON, DISPOSED BETWEEN SAID CONVERGING FACES OF ADJACENT REFRACTORY BLOCKS ADJACENT THEIR OUTER ENDS AND TERMINATING SHORT OF SAID RECESSES AND PROTUBERANCES. 